Organophilic clays have been known as jelling or thickening agents for various fluids such as mineral oils and are particularly useful for thickening oils in the preparation of lubricants such as grease and the like. More specifically, U.S. Pat. Nos. 2,531,427; 2,531,812; and 2,966,506 describe clays that have been modified with organic compounds as thickener for organic fluids. Generally, the process for manufacturing organophilic clays includes adding an onium base, e.g. ammonium, phosphonium, sulfonium, arsonium, stibonium, oxonium, etc. to water slurries of swellable clays causing the onium base to react with the clay to form the organophilic clay product.
In earth boring operations, the use of rotary drilling equipment requires the addition of drilling fluids or muds. These drilling fluids are either made from clays obtainable at the well site or by the addition of hydrophillic colloids of which amine-modified bentonite is the most common. In addition to the organophilic clays, certain other additives including polymers have been used as thickeners for fluids used in the drilling of oil wells. The oil-based drilling muds may be employed where the external or continuous phase of the mud is oil instead of water. The oil-based drilling fluids are useful particularly where drilling is in oil or gas bearing stratum because the oil-based muds will not "drown out" the oil or gas as in the case of a water-based drilling fluid. It is also advantageous to employ an oil-based fluid in drilling through shale formations which are subject to hydration by water. The external phase of the oil-based fluids may include various oils such as petroleum or crude oil distillates, coal tar distillate or residue and other oils such kerosenes, fuel oil, diesel oils and the like.
Organophilic clays made by the aqueous slurry process are useful as thickeners in paints, as well as in mineral oils for the preparation of greases and the like. However, the performance parameters needed for the preparation of these compositions are more critical and require a higher degree of purity of material. The aqueous slurry process provides a grit-free, salt-free product due to the centerfusing, washing and subsequent drying utilized in the processes. The purity of the organophilic clays are less critical, however, where the modified clays are to be used in drilling muds.
Further, the water slurry process also requires dispersing and hydrating the treated clay in deionized or salt free water. The dispersed clay must be stored in order to maintain its hydration and centerfuged to remove any grit remaining in the clay.
The organophilic compound, e.g. quaternary ammonium salts are added to the aqueous dispersion of clay at temperatures ranging from 100.degree. F. to 120.degree. F. The exact quantities of clay and quaternary ammonium salt needed for reaction must be calculated in order to obtain a completely modified clay product. Finally, it is essential that when using the aqueous process the product must be filtered in a filter cake which may contain up to about 80% water, and dried in a stream of warm air. At this point the modified clay may be ground to the desired commercial mesh size and used for a variety of purposes.